Update num_splits heuristic

example/ck_tile/01_fmha/fmha_fwd.cpp

@@ -235,7 +235,7 @@ int override_num_splits_if_necessary(int batch,
     if(num_splits < 1 && p_drop == 0.0f)
     {
         return num_splits_heuristic(
-            batch * nhead * num_m_blocks, props.multiProcessorCount * 2, 32);
+            batch * nhead * num_m_blocks, props.multiProcessorCount * 2, 16);
     }
 
     return num_splits;

example/ck_tile/01_fmha/fmha_fwd.hpp

@@ -829,7 +829,7 @@ Int num_splits_heuristic(Int batch_nhead_mblocks, Int num_SMs, Int max_splits)
     std::vector<float> efficiency;
     efficiency.reserve(max_splits);
 
-    for(Int num_splits = 1; num_splits <= max_splits; num_splits++)
+    for(Int num_splits = 1; num_splits <= max_splits; num_splits *= 2)
     {
         float n_blocks = float(batch_nhead_mblocks * num_splits) / num_SMs;
         float eff      = n_blocks / std::ceil(n_blocks);